short form for "what do you".. usually used in black people because.. long time ago.. african american can't pronounce very well english.. so this word evolved to our times.
"Nothing's the matter." boy, was i getting nervous. "The thing is, i had an operation very recently."
"Yeah? Where?"
"on my wuddayacallit - my clavichord"
- an excerpt from 'The Catcher in the Rye' by J.D. Salinger pg87.